1. Technical Field
The present invention relates to a tunable filter, a light source apparatus, and a spectral distribution measuring apparatus. In particular, the present invention relates to a tunable filter, a light source apparatus, and a spectral distribution measuring apparatus obtaining a predetermined spectral distribution by modulating linearly polarized light of each wavelength region.
2. Related Art
For example, Japanese Patent Application Publication No. H11-101944 discloses an arbitrary spectrum generating light source that converts continuous spectrum light by modulation spectroscopy into a predetermined spectrum and outputs the resulting light. The light source includes a spatial modulator device for an optical beam transmittance at a position corresponding to a light source spectrum image generated by an internal spectroscope, the spatial modulator device including a polarizer and a transmissive liquid crystal element array. This type of light source modulates the spectral characteristic and then synthesizes the wavelength using the internal spectroscope again, thereby outputting light having a predetermined spectrum. There is also a different type of light source apparatus that uses a reflective spatial modulator device, as disclosed in Japanese Patent Application Publication No. 2005-115377, for example.
In recent years, a supercontinuum light source has also started to be used, as disclosed in “Slicing the supercontinuum radiation generated in photonic crystal fiber using an all-fiber chirped-pulse amplification system”: OPTICS EXPRESS Vol. 13, No. 17. Although being a white light source having a continuous spectrum, the supercontinuum light source can be considered as a point light source from the viewpoint of geometrical optics, and has a characteristic that every monochromatic light ray in the output light has a longer coherence than those of a conventional lamp light source.